FUNCTIONAL MR OF THE PRIMARY AUDITORY-CORTEX - AN ANALYSIS OF PURE-TONE ACTIVATION AND TONE DISCRIMINATION

PURPOSE: To use functional MR imaging to measure the effect of frequen cy (pitch), intensity (loudness), and complexity of auditory stimuli o n activation in the primary and secondary auditory cortexes. METHODS: Multiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with con ventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepp ed between 1000, 2000, 3000, or 4000 Hz, and spoken text. The pixels a ctivated by each task in the transverse temporal gyrus (TTG) and the a uditory association areas were tabulated. RESULTS: The pure tone task activated the TTG. The 1000-Hz tone activated significantly more pixel s in the TTG than did the 4000-Hz tone. The 4000-Hz tone activated pix els primarily in the medial TTG, whereas the 1000-Hz tone activated mo re pixels in the lateral TTG. Higher intensity tones activated signifi cantly more pixels than did lower intensity tones at the same frequenc y. The stepped tones activated more pixels than the pure tones, but th e difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditor y association areas. The more complex tasks (stepped tones and listeni ng to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere. CONCLUSION: Auditory stimuli activate the T TG and the association areas. Activation in the primary auditory corte x depends on frequency, intensity, and complexity of the auditory stim ulus. Activation of the auditory association areas requires more compl ex auditory stimuli, such as the stepped tone task or text reading.